Some models do that, I believe is has to do with camera angles and hit boxes. The only fix is to move the camera to a point the model doesn't disapper, or decompile the model, remove the hit boxes and recompile. I had a hat I was making that did this until I was told to do just that, after removing the hit boxes, the hat stopped disappearing.

From my experience, model bones occasionally go really weird when you delete some keys from the graph editor, including the rootTransform, which could just go anywhere. I would suggest copying the latest working key to the last frame of the clip. If that doesn't work, change everything to linear. If that doesn't work, delete the latest working key.

Edit: I actually just noticed, after 3 seconds when the Spy "disappears". He actually doesn't disappear he just moves to where my Camera 1 would be, and my Camera 1 moves to a completely different spot on the map.